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13-16 April 2019

APS April Meeting, Devner

Nils Halverson

12 minutes on CMB-S4

CMB-S4 is a next-generation ground-based cosmic microwave

background (CMB) experiment consisting of dedicated telescopes
equipped with highly sensitive superconducting cameras operating at
multiple sites. CMB-S4 will provide a dramatic leap forward in our
understanding of the fundamental nature of space and time and the
evolution of the Universe. The science goals of CMB-S4 include
illuminating cosmic inflation, measuring the sum of neutrino masses,
searching for relativistic relics in the early universe, characterizing dark
energy and dark matter, and mapping the matter distribution in the
universe. These goals require measurements with unprecedented
sensitivity and control of systematic errors. To address this challenge, the
CMB community has come together to advocate a single comprehensive
“Stage-4” experiment, called CMB-S4, which has been endorsed by the
2014 report of the Particle Physics Project Prioritization Panel (P5)
“Building for Discovery,” and the 2015 NAS/NRC report "A Strategic
Vision for NSF Investments in Antarctic and Southern Ocean Research."

A new generation of extremely sensitive experiments will extend precision measurements of the Cosmic Microwave Background (CMB) anisotropies on large angular scales in polarization, and on arcminute scales in intensity and polarization. The complementary capabilities of ground-based, orbital and sub-orbital balloon borne observatories will provide surveys of the polarized mm-wave sky of with unprecedented sensitivity, fidelity, and spectral resolution, enabling an improved understanding of Galactic emission necessary to realize the scientific potential of the CMB. In this talk we will briefly describe the observational programs underway in the coming decade.

I will describe CMB lensing measurements from current and upcoming CMB experiments. In combination with large-scale structure observables such as clustering and lensing, these will probe the growth of structure over a wide range of redshifts, thus constraining the properties of dark energy and the neutrino masses. Furthermore, CMB lensing measurements can help reduce large-scale structure systematics, such as shear calibration in galaxy lensing.

The SZ Galaxy Cluster Sample and other Legacy Products from the CMB-S4 Experiment

The next generation CMB-S4 experiment will conduct a multifrequency (40-270 GHz) survey of ~40% of the sky at an unprecedented combination of depth and resolution, reaching depths of a few uK-arcmin (~100s uJy) at arcmin-scale resolution in the higher frequency channels. These data will be a tremendous resource for the astronomical community: the deep multifrequency maps will enable the identification of a mass-limited sample of >100,000 galaxy clusters via the Sunyaev-Zel’dovich (SZ) effect, a significant number of higher-redshift protoclusters, galactic sources, and over a million active galactic nuclei (AGN) and dusty star-forming galaxies. Beyond these catalogs the individual frequency maps will be combined to produce maps of the matter distribution as traced by gravitational lensing of the cosmic microwave background, hot gas traced via the thermal SZ, galactic dust, and the cosmic infrared background. The observing cadence will also enable time domain science; each location in the footprint will be imaged more than 1000 times over the course of the multiyear survey enabling characterization of near earth objects, AGN lightcurves, and the discovery of transient objects. In this presentation I will highlight these legacy products, particularly focusing on the scientific impact of the new SZ galaxy cluster sample.

The cosmic microwave background (CMB) radiation is a powerful backlight with which to illuminate structure throughout cosmic history. The thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects, sourced by the scattering of CMB photons off free electrons, directly probe the thermal pressure and density of ionized gas, while gravitational lensing of the CMB directly measures the line-of-sight matter density. Measurements of these effects, which have only been robustly detected within the past decade, will transform our understanding of galaxy formation and evolution in upcoming CMB surveys. I will present predictions for the tSZ and kSZ signals of galaxy and cluster populations at various redshifts derived from state-of-the-art cosmological hydrodynamics simulations, with differing implementations of sub-grid feedback physics due to active galactic nuclei and supernovae. While multiple feedback implementations are able to reproduce the stellar properties of galaxies, their predictions for the tSZ and kSZ signals can be distinguished at high significance by upcoming experiments, including CMB-S4. Next-generation CMB surveys will thus provide crucial input to our understanding of galaxy formation, particularly at high redshift, where other probes have limited signal-to-noise. I will conclude by discussing implications of these measurements for the modeling of baryonic effects on the matter power spectrum, which is amongst the largest systematic uncertainties in cosmological constraints derived from weak gravitational lensing data.

Observations of Cosmic Microwave Background B-mode polarization at large angular scales are a uniquely powerful method to search for primordial gravitational waves, such as those predicted by theories of inflation. A major milestone would be to either detect this signature of gravitational waves or else to set an upper limit on the tensor-to-scalar ratio, r < 0.001, which would rule out the most compelling models of large-field inflation. This goal will be met by Stage-3 experiments currently coming online, the CMB Stage-4 project planned for next decade, as well as new balloon-borne and satellite telescopes. Galactic foregrounds and gravitational lensing of E-mode polarization pose major challenges for these measurements, but are already being addressed by current projects. I will discuss the goals and common design features of experiments targeting the primordial gravitational wave signal, as well as forecasts developed for CMB Stage-4.

Measurements of the CMB have driven our understanding of the universe and the physics that govern its evolution from primordial quantum fluctuations to its present state. They provide the foundation for the remarkable 6-parameter cosmological model, ΛCDM, which fits all cosmological data, although there are some tensions that may possibly hint at new physics. Far from being the last word in cosmology, the model raises deep questions: Is Inflation correct? What is its energy scale? What is the dark matter? What is the nature of dark energy? Are there light sterile neutrinos, or other light relics? This talk will describe progress on the next generation ground-based CMB experiment, CMB-S4, that is being designed to have sufficient sensitivity and control of systematics to make breakthroughs in many of these areas, i.e., to cross critical thresholds in parameter values or show that ΛCDM is incomplete.

Abstract: The 'Stage-4' ground-based cosmic microwave background (CMB) experiment, CMB-S4, consists of dedicated telescopes equipped with highly sensitive superconducting cameras operating at the South Pole, the high Chilean Atacama plateau, and possibly northern hemisphere sites. CMB-S4 will be designed to cross critical thresholds in testing inflation, determining the number and masses of the neutrinos, constraining possible new light relic particles, providing precise constraints on the nature of dark energy, and testing general relativity on large scales. In this contribution, we review the status of the project.

The next-generation ground-based cosmic microwave background experiment, CMB-S4, will achieve new thresholds in the search for the B-mode polarization signature of primordial gravitational waves. To quantify these thresholds, as well as to propose an informed experimental configuration that will reach them, the CMB-S4 forecasting working group has developed a Fisher forecasting machinery targeted towards optimizing tensor-to-scalar parameter constraints in the presence of galactic foregrounds and gravitational lensing of the CMB. In this talk I will describe this framework and explain the uniqueness of this particular approach in basing the forecasts on scalings from actual analyses and multi-year achieved performances of the currently deployed BICEP/Keck series of experiments. In addition, I will detail our work on developing map-level noise simulations, and using various sky models, models of instrumental systematics, and analysis methods to explore the robustness of our findings, which most recently appeared in the CMB-S4 CDT report. Finally, I will talk about employing the Fisher framework in tandem with the simulations work to arrive at the currently proposed CMB-S4 strawman configuration.

The next generation cosmic microwave background (CMB) experiment, CMB-S4, will make unprecedented measurements of secondary anisotropies in the CMB. I will focus on observations of the thermal and kinetic
Sunyaev-Zel’dovich (SZ) effects, which will provide new windows into the thermodynamic properties of galaxy groups and clusters. I will
show how we can constrain important baryonic processes, like feedback, that govern group and cluster formation through the high fidelity SZ
profile measurements from CMB-S4. Additionally, I will describe the prospects to constrain fundamental physics from SZ observations and
how to mitigate the modeling uncertainties associated with the baryonic processes that currently limit these constraints.